Voltage regulating circuit

ABSTRACT

An arrangement for desensitizing dc power supplies to momentary ac power interruptions by incorporating therein an energy-storage network which is charged rapidly to its peak capacity, and then remains on &#39;&#39;&#39;&#39;stand-by&#39;&#39;&#39;&#39; status until an ac power loss occurs. It then supplements the output of the conventional capacitor to maintain steady dc power for a longer period of time than would be otherwise possible.

Umted States Patent 1151 3,697,856 Huang 1451 Oct. 10, 1972 [54] VOLTAGEREGULATING CIRCUIT 3,090,017 5/1963 Novic ..323/DlG. l Inventor: g g,Oxnard Benjamin X [73] Assignee: The United States of America as FOREIGNPATENTS OR APPLICATIONS rNepresenled by the Secretary of the 980,631l/l965 Great Britain ..323/17 avy [22] Filed, 14 1970 PrimaryExaminer-Gerald Goldberg AttorneyRichard S. Sciascia, Howard J. Murray,Jr. [2l] Appl. NO-I 9 ,861 and Q. Baxter Warner [52] US. 01..321/10,323/17,323/1)1o. 1 [57] ABSTRACT [51] Int. Cl....'. ..H02m l/14, H02m 7/12 An arrangement for desensitizing dc power supplies to [58]Field of Search ,.323/17, DIG, 1, 22 SC, 22 T, momentary ac powerinterruptions by incorporating 323 93; 32 2017 0 1 307 23 45 4 thereinan energy-storage network which is charged rapidly to its peak capacity,and then remains on I 56] References Cited stand-by status until an acpower loss occurs. It then supplements the output of the conventionalcapacitor UNITED STATES PATENTS to maintain steady dc power for a longerperiod of l b th 'bl 3,217,233 11/1965 Drusch ..321/27 R erw'se POSS 63,327,202 6/l967 Mills ..'.....323/22 T 3 Claims, 13 Drawing FiguresRECTIFIER FILTER V x BRIDGE 4 REGULATOR OUTPUT ENERGY RESERVOIR CIRCUITPATENTEDncT 10 I972 SHEET 1 or 4 PRIOR ART LOAD

INSTANT OF SOURCE INTERRUPTION t A Fig. la

INSTANT OF SOURCE INTERRUPTION 5 T N m 4 G U A HR m w w m m I 6V C n N Um w E K M FT 8 TE R .L mw IS m TIMI E CE mm U 0 CV A N N PATENTEDUCI 10I972 3 6 97 856 ENERGY RESERVOIR CIRCUIT IOOFFIG.5

1 l 33 msec I* 33 msec Fig. 6b 'Q- VOLTAGE REGULATING CIRCUIT STATEMENTOF GOVERNMENT INTEREST BACKGROUND OF THE INVENTION The rudimentaryfunction of a dc power supply is to receive energy from an ac source,store that energy, and then release it as required by the load. If theac source fails abruptly, the dc output will drop-not suddenly, butexponentially-as the quantity of stored energy'is gradually siphoned bythe load. The time that it takes for the energy todeplete obviouslydepends on the size of the capacitor storing the energy, the amountconsumed by the load, and the minimum voltage required by the load.

It is not unusual for momentary ac power disruptions to occuras theymight during a lightning storm or during frequency adjustments at thepower station. If the disruption is brief enough, the stored energy inthe power supply may be ample to smooth over any effect on the dcvoltage to the load. When the power supply incorporates a basic bridgerectifier-capacitor circuit, it is possible to improve dc outputstability in the event of an ac disruption by increasing the size of theoutput capacitor. This expedient is not practicable, however, for moresophisticated dc power supplies, such as those that make use ofvariable-phase-angle-firing SCRs.

SUMMARY OF THE INVENTION At the present time, dcpower supplies generallyare not designed to maintain continuous and steady voltages duringmomentary disturbances in their ac powertransmission-supply .line. Yet,during lightning storms, or through some line fault, electricaldisturbances can occur within transmission lines that tend to depress dcpower-supply voltages. There are known methods for desensitizing the dcpower supplies to these ,ac

disturbances. One way-if the power supply does not make use of SCRs-isto use larger capacitors in the rectifier circuit. However, this isoften unfeasible economically. The present concept makes use of anauxiliary energy-reservoir network for sustaining the output power forrelatively long periods even when SCRs are employed.

STATEMENT OF THE OBJECTS OF THE INVENTION One object of the presentinvention, therefore, is to provide a dc power supply network havingdecreased sensitivity to momentary, interruptions in the ac source.

Another object of the invention is to provide a dc power supply havingan auxiliary energy-reservoir network incorporated therein.

A further object of the invention is to provide means for sustainingoutput power from a dc supply circuit which includes SCRs therein.

An additional object of the invention is to eliminate the need forutilizing excessively large capacitors in order to maintain output powerfrom a dc supply circuit in the face of momentary disturbances in the acinput thereto.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 (A) is a schematic circuitdiagram of a basic dc power supply network as now known in the art;

FIGS. 1 (B) and (C) are graphs useful in explaining the operation of thenetwork of FIGS. 1 (A);

FIG. 2 is a graph illustrating the effect of using a larger-valuedcapacitor in the network of FIG. 1 (A);

FIG. 3 (A) is a schematic circuit diagram of a conventional dc powersupply network using SCRs;

FIGS. 3 (B) and (C) are graphs useful in explaining the operation of thenetwork of FIG. 3 (A);

FIG. 4 is a block diagram of a dc power supply network designed inaccordance with a preferred embodiment of the present invention;

FIG. 5 is a schematic diagram of the energy reservoir network of FIG. 4;

FIG. 6 (A) is a schematic circuit diagram of a conventional dc powersupply network modified to add an auxiliary capacitor;

FIG. 7 (A) is similar to the circuit of FIG. 6 (A) but with theinvention energy-reservoir network in place of the auxiliary capacitor;and

FIGS. 6 (B) and 7 (B) are graphs useful in explaining the operation ofthe networks of FIGS. 6 (A) and 7 (A), respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENT A bridge rectifier and acapacitor connected as shown in FIG. 1 form the conventionalconfiguration for converting ac voltage to dc voltage. The energystoringcapacitor, C stores and supplies energy to the load. If the ac source isinterrupted, the dc output voltage decays exponentially to zero. Toillustrate, choose an arbitrary voltage, V,, as the minimum valuerequired where V, is the instantaneous voltage across capacitor C at thetime the ac source is interrupted. The time duration, t is given by EQEME-m do Lin where I, is the dc load current. The shortest 1,. results ifthe ac source is interrupted when the instantaneous voltage acrosscapacitor C is V,,,,-,, [FIG. 1(C)]; than Eq. (2) becomes o( min r) daemin Equation (3) shows that when I is fixed, r is exraises V,,,,,, and,therefore, the quantity V,,,,,, V,, the increase in C is dominant inincreasing Q hence, t

FIG. 2 shows the increase in e obtained by using a larger C Curve 1 isfor the large-valued capacitor C Even though a simple method ofextending r is to increase C there are factors that limit the size ofthe energy-storing capacitance.

When selecting a larger-valued capacitance, it becomes necessary toexamine the rise in rectifier cost against the extension of I, obtained.Also, with increasing capacitance, the ratio of initial turn-on currentto rated load current increases. This necessitates opera tion of largerrectifiers at increasingly derated condition, which is inefficient.Also, a larger-valued capacitance increases the response time of the dcpower supply thereby lengthening the flow duration of the turn-oncurrent. Longer flow duration contributes to rectifier failure fromheating.

FIG. 3 (A) is a circuit diagram of a basic silicon controlled rectifier(SCR) dc power supply. The dc output voltage level is controlled by thevariable-phase angle-firing technique, which provides a partial fullwaverectified waveform and requires a very large capacitance to obtain asmoothed-out, limited-ripple waveform; therefore, unlike thetransistor-regulated dc supply circuit, the SCR circuit is not amenableto significant increase in t,. by the mere increase of capacitance. Thisfact is displayed in FIG. 3 (B) which illustrates the limited-ripplevoltage obtained by using a (large) capacitor, C,,. It also shows theextended duration r obtained with the loss of the ac power source.Increasing the capacitance reduces the ripple, as shown in FIG. 3 (C),but V,,,,-,, V, is essentially unchanged and duration t increasesslightly. The limitations on extending 1,. in a basic dc power-supplycircuit are therefore more severe in a power circuit using SCRs insteadof transistors.

With either circuit, however, it is possible to supplement the Qavailable in the basic powersupply circuit-and thus t,.with anenergy-reservoir circuit, designed in accordance with the principles ofthe present invention. One preferred embodiment is illustrated in FIGS.4 and 5 of the drawings.

The basic principle of this circuit is to charge an energy-storingcapacitor at a high voltage and release this energy to the load duringmomentary ac power loss. The energy storing C is charged rapidly to itspeak capacity during normal operations of the ac power source. Thereservoir circuit of FIGS. 4 and 5 remains on standby status andconsumes very little power. At the instant of ac power loss, thereservoir circuit 10 supplies Q to supplement Q, and maintain Vthroughout the outage. The capacitance C can be calculated by modifyingEq. (3):

aux"

where r,,,, is the extended duration of dc voltage without insertion ofthe energy reservoir circuit; and V,, is the peak value to which C canbe charged.

The current limiter 12 in the auxiliary circuit is used to (I) preventdamage to the rectifier D by the initial charging current and (2)protect the active elements in the control circuit from the high currentfrom the rectifier transformer during a malfunction of dc power supply.

During the initial charging, the' voltage of C usually is lower than theoutput voltage, V,,. Rectifier D is used to prevent damage totransistors Q, and Q: from the current flowing from point 3. The voltagedifference, V V,), determines the selection of the maximum rating of Vthe voltage of the power transistor 0,. The comparison circuit 14 ispresent to sense the voltage drop and to fumish the actual signal tooperate the control circuit 16. The sensing voltage should be adjustedin such a position that the energy-reservoir circuit 10 remains onstandby status in normal operation. The control circuit 16 adjusts theflow rate of Q as required by the load to maintain the output voltageThe energy-reservoir circuit is connected to the basic power supply asshown in FIG. 4. The reservoir circuit 10 offers considerable latitudein the selection of the value of the energy-storing capacitance and theoperating voltage. This flexibility is not offered in the basic dcpower-supply circuit because the required output voltage fixes thevoltage across theenergy-storing capacitor, C the method of obtainingthe larger Q, is limited to increasing C, and a larger C, is accompaniedby undesirable effects, such as excessive inrushing of turn-on current.

The power ratings of the components in the reservoir circuit 16 can bemodest because the average power is low, although the peak energydelivered momentarily may be appreciable. The auxiliary reservoircircuit,

even with the use of a large energy-storing capacitor C does not reducethe response time of the basic power supply because the one isindependent of the other.

FIGS. 6 and 7 illustrate the advantages obtainable by utilizing anetwork embodying the principles of the present invention. Simply addinga capacitor C as in FIG. 6 (A) extends the dc output level by 12 msec(FIG. 6 (8)). However, utilizing the energy-reservoir network 10 ofFIGS. 4 and 5 in the circuit of FIG. 7 (A) extends the dc output levelto 38 msec (FIG. 7 (8)), using the same value of capacitor. This is anincrease of over 200% as compared to the conventional technique of FIG.6 (A).

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

lclaim:

1. An energy reservoir circuit for desensitizing a dc. power supply tomomentary ac. power interruptions comprising:

a charge storing network connected in parallel with the main rectifyingand filtering network of a dc. power supply, and storing networkcomprising;

a transformer;

a current limiter connected in series with the secondary of saidtransformer;

a rectifier connected in series with said current limiter;

a capacitor connected in parallel with the transformer secondary,current limiter and rectifier;

discharge rate controlling means connected in se- 3. A circuit asrecited in claim 2 wherein said actuatwlth said capacltori and ing meansis comprised of a comparison circuit conactuating means connected tosaid discharge rate controlling means. 2. A circuit as recited in claim1 wherein said 5 discharge rate controlling means comprises a powertransistor in series withaprotective diode.

nected across the output of the energy reservoir for sensing a voltagedrop in the output from the main rectifying and filtering network of adc. power supply.

1. An energy reservoir circuit for desensitizing a d.c. power supply tomomentary a.c. power interruptions comprising: a charge storing networkconnected in parallel with the main rectifying and filtering network ofa d.c. power supply, and storing network comprising; a transformer; acurrent limiter connected in series with the secondary of saidtransformer; a rectifier connected in series with said current limiter;a capacitor connected in parallel with the transformer secondary,current limiter and rectifier; discharge rate controlling meansconnected in series with said capacitor; and actuating means connectedto said discharge rate controlling means.
 2. A circuit as recited inclaim 1 wherein said discharge rate controlling means comprises a powertransistor in series with a protective diode.
 3. A circuit as recited inclaim 2 wherein said actuating means is comprised of a comparisoncircuit connected across the output of the energy reservoir for sensinga voltage drop in the output from the main rectifying and filteringnetwork of a d.c. power supply.